Hey there tearle176,
We understand your MacBook Pro is not recognizing SD cards as expected. However, it does show an error when it is not ejected while taking the card out. We'll be happy to help.
To begin, take a few moments to review this page: About the SD and SDXC card slot on your Mac
This covers more about how SD cards can be used. It does mention that it is for Macs with built-in SD card readers, but the steps should be similar for your setup.
Note that you may need to format your SD card. Check out the steps from the section "Can I use Disk Utility to reformat an SD card?".
If you still experience issues, try using a different adapter if possible.
Cheers!